1. Field of the Invention
This invention is in the field of gasoline engines and specifically in the field of improvements in the cold starting and hot stopping of gasoline engines.
2. Description of the Prior Art
When a gasoline engine is to be started cold, gasoline, considerably in excess of that needed to create a spark ignitable air-fuel vapor mixture, is mixed with the incoming air in the carburetor because only a small portion of the liquid gasoline evaporates when the engine is cold, and it is only the evaporated gasoline portions which mix with the air to form the ignitable air-fuel vapor mixture. To evaporate liquid gasoline requires that heat be transferred to the gasoline at least equal to the latent heat of evaporation of those gasoline portions evaporating. In a cold engine, which is not firing, the only static sources of the heat energy needed for gasoline evaporation are, the metal of the carburetor, manifolds, valves, cylinders, and pistons of the engine, the incoming air, and the unevaporated gasoline portions. When the ambient air temperature, and hence the engine metal temperatures, are warm enough that these static heat energy sources can evaporate sufficient of the liquid gasoline to create an ignitable air-fuel vapor mixture the engine will start upon the first pair of cranking revolutions. At air temperatures below this "warm start" temperature the engine does not start upon the first pair of cranking revolutions and the gasoline evaporated during such non-firing cranking revolutions is pumped out the engine exhaust valve and discharged into the atmosphere as unburned hydrocarbons. In addition the heat energy extracted statically from the metal parts of the engine to evaporate these discharged unburned hydrocarbons is also thrown away and the temperature of these metal parts is reduced thereby. Hence during subsequent, non-firing cranking revolutions less heat is available for gasoline evaporation and less liquid gasoline is evaporated from these static sources and, if heat energy for evaporation were available only from these static sources a gasoline engine would either start firing on the first pair of cranking revolutions or it would not start firing on any of the subsequent cranking revolutions. Experience shows, however, that a cold engine can be started by prolonged cranking and that the number of cranking revolutions needed to start the engine firing generally increases as the engine is colder, as shown, for example, in the article entitled, "Effect of Fuel Volatility on Starting and Warm-up of New Automobiles," by Messrs. Moore, Young and Toulmin, Transactions of the Society of Automotive engineers, Volume 65, p. 692, 1957. During the non-firing cranking revolutions the electric starter motor overcomes engine friction forces and compresses and expands the air-fuel vapor mixture. The work of compressing the air-fuel vapor mixture increases its temperature above the value prevailing in the engine intake manifold, the maximum rise in temperature occurring when maximum compression pressure is attained. Thereafter during expansion the temperature of the air-fuel vapor mixture decreases from this maximum attained value and would again reach the value prevailing in the engine intake manifold if no liquid gasoline evaporation occurred and if no heat transfer took place between the air-fuel vapor mixture and the adjacent, colder engine parts (piston, cylinder, valves, etc.). Hence, in general, the air-fuel vapor mixture is hotter than the adjacent engine parts throughout most of the compression and expansion processes and, in consequence, heat energy is transferred from this hotter air-fuel vapor mixture to the adjacent colder piston, cylinder wall, cylinder head, valves, etc. causing an increase in the temperature of these engine parts. That portion of the cranking work of the electric starter motor devoted to overcoming the friction force between the cylinder wall and the piston and rings reappears as increased energy content and hence increased temperature of these engine parts. This "dynamic" source of heat energy from the engine cranking work of the electric starter motor can evaporate additional portions of liquid gasoline and, when a sufficient quantity of this dynamic heat energy has been stored, by continued cranking, in the internal metal surfaces of the engine combustion chamber, sufficient additional gasoline is evaporated to create an ignitable air-fuel vapor mixture and the engine may then start firing. We may now define a "cold" start of a gasoline engine as a start wherein the dynamic heat energy thus stored during cranking is required to cause sufficient additional gasoline evaporation that an ignitable mixture is created and the engine starts firing. The devices of this invention function to improve the starting of gasoline engines under "cold" starting conditions as thus defined.
Whenever gasoline is evaporated during a cranking revolution without the engine having started firing in consequence, not only is the thusly evaporated gasoline discarded into the exhaust manifold and thereafter useless for the starting of the engine, but additional detriment to starting results from the corresponding heat energy, from both static and dynamic sources, being also discarded and being thereafter unavailable to aid in starting the engine on subsequent cranking revolutions. It is thus seen that a better way to cold start a gasoline engine is to crank the engine, without gasoline admission, until a sufficiently high temperature of the internal metal surfaces of the engine combustion chamber is reached that, when gasoline is admitted, enough evaporates to create an ignitable air-fuel vapor mixture and in consequence the engine commences firing immediately upon the admission of gasoline. In this way the amount of gasoline needed for cold starting can be reduced and the duration of cranking required to start the engine is reduced. It is an object of this invention to automatically accomplish this improved manner of cold starting gasoline engines.
The engine choke acts to supply the excess gasoline needed for cold starting by restricting incoming air flow upstream of the carburetor and in this way increasing the pressure difference between the carburetor float bowl and the air flowing through the venturi and in consequence a greater quantity of gasoline flows through the carburetor jets into the incoming air. The amount of excess gasoline thus metered into the air increases as the choke is set more nearly closed. At wide open choke, no excess gasoline is metered. Hence, the quantity of excess gasoline metered during cold starting is controlled by controlling the choke. The invention described in U.S. Pat. No. 3,732,856 accomplishes the cold starting objects described herein above by automatically holding the choke wide open, and hence inoperative, during the early period of cranking and then allowing the choke to close after the cranking work has sufficiently increased the temperatures of various interior engine surfaces that the excess gasoline, admitted upon choke closure, is adequately evaporated to produce an ignitable air-fuel vapor mixture immediately or shortly after closing the choke. In this way the excess gasoline flow caused by the choke is withheld from the engine until it is ready to start. The invention described herein accomplishes the cold starting objects described herein in an improved manner by not only withholding the excess gasoline flow caused by the choke but also by withholding any gasoline flow through the gasoline metering device and delivery jets since the gasoline flow passage is altogether closed by the valve portion of the devices of this invention.
Many gasoline engines do not stop running when the ignition is turned off because an ignition source, other than the electric spark, exists somewhere in the engine combustion chamber. Frequently this extra source of ignition is a hot portion of the combustion chamber surface such as the ceramic insulator of the spark plug, the engine exhaust valve head, deposits formed on the combustion chamber surface from portions of the fuel and lubricating oil used in the engine. In some cases this extra source of ignition may be compression ignition occurring at low engine speed. Whatever the source of this extra ignition it prevents the prompt stopping of the engine when desired which is not only inconvenient but may also be hazardous at times. Additionally this running-on of the engine after the electric spark has been turned off may contribute additional unburned hydrocarbons as smog materials into the atmosphere. Commonly, only a few of the cylinders of a multicylinder engine continue to fire after the electric spark has been turned off and the gasoline in the non-firing cylinders is discharged as unburned hydrocarbons to the engine exhaust. By fully stopping the flow of gasoline to the engine at the time the electric spark ignition is turned off the prompt stopping of the engine is assured, no matter what extra sources of ignition there may be, and no additional unburned hydrocarbons are discharged into the atmosphere. This invention accomplishes this stoppage of gasoline flow by closure of the valve element at ignition turn off as described previously herein, and, in this manner, accomplishes these additional beneficial objects relating to the stopping of the engine.